Broadband cholesteric polarizer and an optical device employing the same

Abstract

A broadband cholesteric polariser includes at least one pair of adjacent layers. The at least one pair includes a cholesteric layer and a compensating layer. The compensating layer has a refractive index perpendicular to the compensating layer greater than a refractive index oriented within the compensating layer.

What is claimed is: 
     
       1. A broadband cholesteric polariser comprising at least one pair of adjacent layers, wherein the at least one pair of adjacent layers comprises a cholesteric layer and a compensating layer, the compensating layer having a refractive index perpendicular to the compensating layer greater than a refractive index oriented within the compensating layer, and wherein the at least one pair of adjacent layers comprises a plurality of pairs of adjacent layers containing cholesteric layers and compensating layers and each of the cholesteric layers has a different average pitch.   
     
     
       2. A light source comprising at least one light emitter, and a polariser as claimed in claim 1 for polarising light from the at least light emitter. 
     
     
       3. A polariser as claimed in claim 1, wherein the cholesteric layers alternate with the compensating layers. 
     
     
       4. A polariser as claimed in claim 1, wherein each of the cholesteric layers has a substantially constant pitch. 
     
     
       5. A polariser as claimed in claim 4, wherein the pitches of the cholesteric layers increase monotonically from a first surface to a second surface of the polariser. 
     
     
       6. A polariser as claimed in claim 1, wherein each of the cholesteric layers has a graded pitch. 
     
     
       7. A polariser as claimed in claim 6, wherein the average pitches of the cholesteric layers increase monotonically from a first surface to a second surface of the polariser. 
     
     
       8. A polariser as claimed in claim 1, wherein all of the layers are formed in a single film of cholesteric material. 
     
     
       9. A polariser as claimed in claim 8, wherein the compensating layer is in a non-cholesteric state. 
     
     
       10. A polariser as claimed in claim 9, wherein the compensating layer is in a homeotropic state. 
     
     
       11. An optical device comprising a light source and a cholesteric polariser comprising a layer of graded pitch cholesteric material whose pitch increases monotonically from a first surface to a second surface thereof, wherein the first surface is disposed so as to receive light from the light source.